This invention is concerned with a method of manufacturing a parison of molten glass for subsequent moulding into a glass container and with parison moulding apparatus for moulding such parisons.
In the manufacture of glass containers, it is common practice to mould a gob of molten glass into an intermediate shape, known as a parison, in a first mould and then to transfer the parison to a second mould in which the parison is moulded into a glass container. One method of manufacturing such parisons which have wide necks is described in G.B. patent specification No. 1491859. In this method, a mould having a mould cavity which defines the desired shape of the parison is assembled. The mould, which has its neck facing upwardly, comprises a one-piece lower mould portion defining a lower portion of the mould cavity. The lower mould portion is mounted for movement upwardly into a mould-assembled position thereof or downwardly into a parison-releasing portion thereof. The mould also comprises a dividable neck ring defining a neck portion of the mould cavity. The neck ring comprises two neck ring halves which are mounted on a carriage for horizontal movement between an engaged position of the halves in which they cooperate in defining the neck portion and a separated position of the halves in which the parison can be removed. The mould also comprises a dividable central mould portion which comprises two halves which are movable horizontally to an engaged position in which the halves engage one another, the lower mould portion, and the neck ring to cooperate in defining the mould cavity and to a separated position in which the parison can be removed.
In the method of G.B. patent specification No. 1491859, when the mould has been assembled, a gob of molten glass is introduced into the mould cavity through the neck ring. Then, a vertically-disposed plunger is moved horizontally into alignment with the neck ring and then downwardly through the neck ring and into the mould cavity. The plunger presses the glass into conformity with the mould cavity thereby forming the parison. The plunger is then withdrawn from the mould. Then, the two halves of the central mould portion are moved to their separated position and the lower mould portion is moved downwardly clear of the parison. The parison is now supported by the neck ring which is moved horizontally to carry away the parison.
In the method of G.B. patent specification No. 1491859, the neck ring defines the sealing surface of the neck portion of the mould cavity, the sealing surface being the uppermost surface of the parison against which a cap of the container seals the completed container. This method, however, cannot be used to make narrow neck parisons because the neck ring would not be sufficiently wide to allow the gob to enter the mould cavity. Instead, for a narrow neck parison, the gob is introduced into the lower mould portion before assembly of the mould, the mould is then assembled and the method then continued as for a wide neck parison. An example of this method is described in European patent specification No. 0102001. This method, however, has the disadvantages that the time between gob loading and pressing is increased slowing up the moulding process and that the glass is in contact with the lower mould portion longer than with the remainder of the mould so that the parison has less temperature uniformity. In U.S. Pat. No. 4,288,240, a modification of the method of the aforementioned G.B. patent specification No. 1491859 is illustrated, in this modification a gob guide is engaged by the neck ring and serves to guide gobs through the neck ring into the mould cavity. The gob guide defines the sealing surface of the mould cavity. However, in this modification, the width of the gob guide is limited making gob feeding less easy.
It is an object of the present invention to provide a method of the type described of manufacturing a narrow neck parison in which the gob can be easily loaded through the neck ring.